1. Field of the Invention
The present invention relates to a method for manufacturing an ink-jet head that ejects ink to a record medium.
2. Description of Related Art
Japanese Patent Unexamined Publication No. 11-251353 discloses a semiconductor device that includes a flexible circuit board and an IC chip. The flexible circuit board has a polyimide, which is an insulating member, and a copper foil formed in a circuit pattern on the polyimide. The IC chip is mounted on a face of the flexible circuit board having the copper foil thereon so as to be electrically connected to the copper foil. In this semiconductor device, the polyimide of the flexible circuit board has through holes. Portions of the copper foil exposed through the through holes constitute electrode parts of the semiconductor device. The through hole has a tapered shape whose diameter is increasing from the face on which the copper foil is formed toward an opposite face. When, in this state where the through hole has a tapered shape, a solder ball is disposed within the through hole so that an electrode part of the semiconductor device is connected via the solder ball to an electrode part of a mother board, the solder ball obtains improved crack resistance because thermal stress caused by difference in thermal expansion coefficient between the semiconductor device and the mother board does not so much concentrate on the solder ball.
However, the aforesaid patent document does not mention the relationship between the taper angle of the through hole and the thickness of the polyimide in which the through hole is formed. Therefore, when the polyimide in which the through hole is formed has a relatively large thickness or when the through holes are formed at a high density in order to realize a high-resolution printing, openings of neighboring through holes on a face of the polyimide opposite to the face on which the copper foil is formed may interfere with or become so close to each other. If the openings of the through holes interfere with or become so close to each other, a solder ball disposed in a through hole may adhere to an uncorresponding electrode part of the mother board, e.g., an electrode part neighboring a corresponding electrode part, or solder balls come in contact with each other, to thereby cause a short circuit between electrode parts.
In an ink-jet head used in an ink-jet printer, etc., ink supplied from an ink tank is distributed to a plurality of pressure chambers and pulse pressure is selectively applied to the respective pressure chambers to thereby eject ink from nozzles. As a means for selectively applying pressure to the pressure chambers, an actuator unit having laminated ceramic piezoelectric sheets may be used.
As an example of such actuator unit, known is an actuator unit in which a plurality of laminated piezoelectric sheets extending over many pressure chambers are sandwiched between a common electrode extending over a plurality of pressure chambers and individual electrodes corresponding to the respective pressure chambers (see U.S. Patent Application No. 2003156157). When a drive voltage is supplied from a flexible printed circuit (FPC) to an individual electrode that is electrically connected to the FPC so that the potential of the individual electrode is differentiated from that of the common electrode, a portion of the piezoelectric sheets sandwiched between the individual electrode and the common electrode to be polarized in their thickness direction expands and contracts in their thickness direction by a piezoelectric effect. Thereby, the volume of the corresponding pressure chamber is changed, and ink can be ejected from a nozzle communicating with the pressure chamber toward a record medium. When this type of ink-jet head adopts the technique disclosed in the aforementioned Japanese Patent Unexamined Publication No. 11-251353 in order to bond the individual electrodes and the FPC, a short circuit between individual electrodes may similarly be caused.